The electrodeless lamps with which this invention is concerned in general comprise a lamp envelope containing a plasma-forming medium. To operate the lamps, the medium in the envelope is excited with microwave, R.F. or other electronic energy, thereby generating a plasma, which emits radiation in the ultraviolet, visible or infrared part of the spectrum. The lamp is typically mounted in a microwave chamber having an opening which is covered by a conductive mesh which is effective to retain microwave energy in the chamber while allowing light emitted by the lamp to escape.
If the opening is not covered with the conductive mesh, large quantities of microwave energy escape into the environment and endanger nearby personnel. The possibility exists that the mesh could be omitted during reassembly following repair or replacement of lamp components, and the need exists to prevent accidents arising from a failure to assemble or use a lamp properly.